Among systems for displaying maps to a destination, there are systems for extracting and displaying map information of areas along a route to the destination (e.g. JP-A No. 314634/2000). There is also a technology for setting a user-designated area range for map information extraction so that area includes a geographic point specified by the user (JP-A No. 12962/2001).
Map information is generally stored in rectangular coordinates on a recording medium. However the actual surface of the earth is spherical so even if extracting a pre-established area with a designated width from the route, a longitudinal error may occur due to the route latitudinal position. In other words, the related art had the problem that map information may be extracted in a narrower or wider range than the desired location for display.
When extracting information of specified area based on the shape of the road centerline along the route, a polygon representing that area may possess a lot of vertexes. So one background system needs an extremely large amount of time for judgment processing of information in an internal unit of the area from the recorded map information. Then it may be difficult to achieve enough performance to handle practical service needs.
Further, standard map information provided only for peripheral areas on the established route and may not include information such as rest stops and side-trip points along the way. The user therefore may have to once again make a search to obtain the desired information. A method is available for providing detailed map information by enlarging an area specified by the user on the map displaying the route. However no area suggestion is provided by this method, so the user may have to deal with the troublesome task of selecting an appropriate area allowing supply of detailed map information.